|Publication number||US7145986 B2|
|Application number||US 10/838,893|
|Publication date||Dec 5, 2006|
|Filing date||May 4, 2004|
|Priority date||May 4, 2004|
|Also published as||US20050249331|
|Publication number||10838893, 838893, US 7145986 B2, US 7145986B2, US-B2-7145986, US7145986 B2, US7145986B2|
|Inventors||James A. Wear, Robert A. Washenko|
|Original Assignee||General Electric Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Referenced by (31), Classifications (28), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates generally to x-ray detectors, and in particular, to a cadmium zinc telluride (CZT) detector used for quantitative x-ray imaging.
Measurements of the x-ray absorption by an object at two different x-ray energies can reveal information about the composition of that object as decomposed into two selected basis materials. In the medical area, the selected basis materials are frequently bone and soft tissue. The ability to distinguish bone from surrounding soft tissue allows x-ray images to yield quantitative information about in vivo bone density for the diagnosis of osteoporosis and other bone disease.
Selecting different selected basis materials allows dual energy x-ray measurements to be used for other purposes. For example, dual energy x-ray measurements can be used for the analysis of body composition by distinguishing between fat and lean tissue, or for baggage scanning by distinguishing between explosive and non-explosive materials.
Cadmium zinc telluride (CZT) detectors may be used to measure x-rays passing through a measured object in dual energy x-ray systems. Such CZT detectors release an electrical charge for each incident photon proportional to the photon energy and thus allow separate measurement of high and low energy x-rays as sorted by pulse height.
Generally, a CZT detector employs a number of separate crystals of CZT, each having a front and rear surface electrode to detect x-rays within a pixel defined by the area of the crystal. Constructing a CZT detector requires the assembly of many separate CZT crystals which can be difficult. High-resolution detectors having smaller pixel sizes require smaller crystals, exacerbating the problem of assembly.
The present invention provides a high resolution CZT detector constructed of a monolithic crystal of CZT having multiple electrodes placed on one face to define multiple pixels. The monolithic design eliminates the assembly problems caused by the use of many separate crystals but normally does not provide the signal quality associated with separate crystal designs.
While the present inventors do not wish to be bound to a particular theory, they believe that this loss of signal quality is caused by x-rays striking between the electrode defined pixels (in “gutter regions”) which liberates charge carriers that then migrate unpredictably into adjacent pixels corrupting the measurements at those pixels.
For this reason, the present invention provides for an x-ray blocking mask to cover the gutter regions.
These particular features, objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.
Referring now to
A cathode 22 is applied to the front surface 14 of the CZT crystal 12, and an anode 24 is applied to the rear surface 20 of the CZT crystal 12 to provide a biasing electrical field between them. Generally, the cathode 22 will cover the entire front surface 14 but the anode will cover only a small area centered on the rear surface 20. Both the cathode 22 and anode 24 may be applied directly to the CZT crystal 12, for example, by sputtering, and are preferably formed of a conductive metal such as platinum. The front surface 14 of the CZT crystal 12 may also be protected by a light, opaque, x-ray transparent material such as aluminized Mylar. Mylar is a registered trademark of E.I. Du Pont De Nemours and Company Corporation of Wilmingtion Del.
The anodes 24 are separated by a gutter region 25. In one embodiment of the invention, the anodes 24 are approximately 1.5 by 2.5 millimeters in area and the gutter regions 25 are approximately 150–200 microns wide. The gutter regions 25 serve to electrically isolate the anodes 24 to permit independent measurement of bursts of charge released between the cathode 22 on front surface 14 and the anodes 24 on the rear surface 20 along axis 23 for each pixel region 15. Weak electric fields in this inter-pixel (gutter) region are responsible for inefficient charge collection. Although the preferred embodiment may use steering electrodes (not shown), there is always a region (typically 0.1–0.2 mm) in which charge is split between two pixels, due to the finite width of charge deposition created by x-ray absorption.
To promote efficient collection of charge deposited in the crystal 12, a bias voltage controlled via input 57 to bias voltage source 31 is applied across the opposed cathode 22 and anodes 24 of each pixel region 15 producing an electrical field 32. X-ray photons 16 passing through cathode 22 on the front surface 14 enter the monolithic crystal 12 to liberate charge carriers 34 (shown here as electrons) which are then collected by anodes 24 on the rear surface 20 and conducted via separate leads 36 for each pixel region 15 to a ground referenced charge integrator 38. The amount of charge liberated by each photon 16 is indicative of the energy of the x-ray photon 16. Outputs from the charge integrators 38 are received by one or more processing computers 40 connected via network 50 that may produce a quantitative image of the x-ray photons 16 according to techniques well known in the art.
In contrast to x-ray photons 16 striking within the pixel regions 15, x-ray photons 18 passing into the monolithic crystal 12 at gutter region 25 will produce charge carriers 39, that may migrate into a pixel region 15 to be collected by anode 24 on the rear surface 20. These charge carriers 39 degrade the quantitative accuracy and spatial resolution of a monolithically designed detector system 10, adding an effective noise component to the charge collected from x-ray photons 16.
Referring now to
It will be recognized that other x-ray attenuating materials may be used for the mask 44 other than tungsten. However, the tungsten is readily machined via laser cutting to the appropriate grid size. Registration points may be placed on the front surface 14 to allow the registration of the mask 44 with the gutter regions 25 during manufacture.
Referring now also to
The steering electrodes 30 surrounding each anode 24 (and equal area anode contact 28) describe by their perimeter a pixel region 15 associated with each anode contact 28. The steering electrodes are not necessary to the design and pixels regions may be defined by the combination of mask and shape of electric field between anode and cathode with or without steering grid. The pixel regions 15 describe areas which may independently detect x-ray photons 16 to produce a quantitative detection value that will be mapped to individual pixels in a resultant image.
In the embodiment shown in
Referring now to
Referring still to
Referring now to
The present invention is applicable not only to polygonal electrode regions, but other shapes as well.
It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5229597 *||Jun 26, 1991||Jul 20, 1993||Kabushiki Kaisha Toshiba||Image pickup device suitable for dimensional measurement image pickup equipment including a vernier pixel array|
|US5677539 *||Oct 13, 1995||Oct 14, 1997||Digirad||Semiconductor radiation detector with enhanced charge collection|
|US5821539 *||Apr 23, 1997||Oct 13, 1998||Siemens Aktiengesellschaft||Fast operating radiation detector and method for operating same|
|US5841832||Sep 26, 1997||Nov 24, 1998||Lunar Corporation||Dual-energy x-ray detector providing spatial and temporal interpolation|
|US5841833||Mar 11, 1997||Nov 24, 1998||Lunar Corporation||Dual-energy x-ray detector providing spatial and temporal interpolation|
|US5905264 *||Aug 4, 1997||May 18, 1999||Imarad Imaging Systems Ltd.||Semiconductor detector|
|US6028313 *||Dec 31, 1997||Feb 22, 2000||Mcdaniel; David L.||Direct conversion photon detector|
|US6034373 *||Dec 11, 1997||Mar 7, 2000||Imrad Imaging Systems Ltd.||Semiconductor radiation detector with reduced surface effects|
|US6037595||Oct 14, 1997||Mar 14, 2000||Digirad Corporation||Radiation detector with shielding electrode|
|US6072181 *||Jul 21, 1995||Jun 6, 2000||Imperial College Of Science||Ionizing radiation detector|
|US6201247 *||Apr 2, 1998||Mar 13, 2001||Picker International, Inc.||Line source for gamma camera|
|US6272207 *||Feb 18, 1999||Aug 7, 2001||Creatv Microtech, Inc.||Method and apparatus for obtaining high-resolution digital X-ray and gamma ray images|
|US6298113 *||Feb 7, 2000||Oct 2, 2001||General Electric Company||Self aligning inter-scintillator reflector x-ray damage shield and method of manufacture|
|US6459086 *||Nov 24, 2000||Oct 1, 2002||Koninklijke Philips Electronics, N.V.||Digital peak detector for radiation detection systems|
|US6586742 *||Mar 1, 2002||Jul 1, 2003||Mats Danielsson||Method and arrangement relating to x-ray imaging|
|US6696686 *||Jun 5, 2000||Feb 24, 2004||Elgems Ltd.||SPECT for breast cancer detection|
|US6765213 *||Jul 30, 2001||Jul 20, 2004||Imarad Imaging Systems Ltd.||Gamma-ray detector for coincidence detection|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US7564940 *||Jul 15, 2004||Jul 21, 2009||Koninklijke Philips Electronics N.V.||Radiation mask for two dimensional CT detector|
|US7728301 *||Mar 4, 2009||Jun 1, 2010||Kabushiki Kaisha Toshiba||X-ray detector|
|US8084746 *||Apr 20, 2007||Dec 27, 2011||Multi-Dimensional Imaging, Inc.||Radiation detector and detection method having reduced polarization|
|US8521253||Oct 29, 2007||Aug 27, 2013||Spectrum Dynamics Llc||Prostate imaging|
|US8565860||Jul 10, 2003||Oct 22, 2013||Biosensors International Group, Ltd.||Radioactive emission detector equipped with a position tracking system|
|US8571881||May 17, 2007||Oct 29, 2013||Spectrum Dynamics, Llc||Radiopharmaceutical dispensing, administration, and imaging|
|US8606349||Oct 31, 2007||Dec 10, 2013||Biosensors International Group, Ltd.||Radioimaging using low dose isotope|
|US8610075||Nov 13, 2007||Dec 17, 2013||Biosensors International Group Ltd.||Radioimaging applications of and novel formulations of teboroxime|
|US8615405||Oct 31, 2007||Dec 24, 2013||Biosensors International Group, Ltd.||Imaging system customization using data from radiopharmaceutical-associated data carrier|
|US8620046||Jan 8, 2012||Dec 31, 2013||Biosensors International Group, Ltd.||Radioactive-emission-measurement optimization to specific body structures|
|US8620679||Oct 31, 2007||Dec 31, 2013||Biosensors International Group, Ltd.||Radiopharmaceutical dispensing, administration, and imaging|
|US8644910||Jul 19, 2006||Feb 4, 2014||Biosensors International Group, Ltd.||Imaging protocols|
|US8676292||Jan 23, 2007||Mar 18, 2014||Biosensors International Group, Ltd.||Multi-dimensional image reconstruction|
|US8748826||Jun 10, 2013||Jun 10, 2014||Biosensor International Group, Ltd.||Radioimaging methods using teboroxime and thallium|
|US8748827||Jul 22, 2013||Jun 10, 2014||Biosensors International Group, Ltd.||Method and system of optimized volumetric imaging|
|US8837793||Jan 9, 2012||Sep 16, 2014||Biosensors International Group, Ltd.||Reconstruction stabilizer and active vision|
|US8894974||May 11, 2007||Nov 25, 2014||Spectrum Dynamics Llc||Radiopharmaceuticals for diagnosis and therapy|
|US8909325||Jul 11, 2001||Dec 9, 2014||Biosensors International Group, Ltd.||Radioactive emission detector equipped with a position tracking system and utilization thereof with medical systems and in medical procedures|
|US9040016||Jul 19, 2007||May 26, 2015||Biosensors International Group, Ltd.||Diagnostic kit and methods for radioimaging myocardial perfusion|
|US9075152 *||Aug 2, 2012||Jul 7, 2015||Canon Kabushiki Kaisha||Detection apparatus configured to detect soft X-ray radiation and detection system configured to detect soft X-ray radiation|
|US9159765 *||Aug 2, 2012||Oct 13, 2015||Canon Kabushiki Kaisha||Apparatus for detecting soft X-ray radiation and X-ray detection system including such apparatus|
|US9275451||Dec 20, 2007||Mar 1, 2016||Biosensors International Group, Ltd.||Method, a system, and an apparatus for using and processing multidimensional data|
|US9316743||Nov 18, 2013||Apr 19, 2016||Biosensors International Group, Ltd.||System and method for radioactive emission measurement|
|US9370333||Dec 26, 2013||Jun 21, 2016||Biosensors International Group, Ltd.||Radioactive-emission-measurement optimization to specific body structures|
|US20060227930 *||Jul 15, 2004||Oct 12, 2006||Mattson Rodney A||Radiation mask for two dimensional ct detector|
|US20090022270 *||Apr 11, 2006||Jan 22, 2009||J. Morita Manufacturing Corporation||X-Ray Image Sensor and X-Ray Imaging Apparatus Using the Same|
|US20090242781 *||Mar 4, 2009||Oct 1, 2009||Kabushiki Kaisha Toshiba||X-ray detector|
|US20100116998 *||Apr 20, 2007||May 13, 2010||Hadong Kim||Radiation detector and detection method having reduced polarization|
|US20130032724 *||Feb 7, 2013||Canon Kabushiki Kaisha||Detection apparatus configured to detect soft x-ray radiation and detection system configured to detect soft x-ray radiation|
|US20130032726 *||Aug 2, 2012||Feb 7, 2013||Canon Kabushiki Kaisha||Apparatus for detecting soft x-ray radiation and x-ray detection system including such apparatus|
|US20150131776 *||Nov 12, 2014||May 14, 2015||Samsung Electronics Co., Ltd.||Radiation detector and computed tomography apparatus using the same|
|U.S. Classification||378/98.8, 257/E27.146, 378/98.9, 250/370.09, 250/370.13, 378/53, 257/E31.015|
|International Classification||H01L25/00, H05G1/64, H01L31/0296, H01L31/09, G01N23/087, G01J1/00, A61B6/00, G01T1/24, H01L27/14, G01T1/36, H01L27/146, G01B15/02|
|Cooperative Classification||G01T1/241, G01T1/366, H01L27/14623, H01L31/0296, H01L27/14676|
|European Classification||G01T1/24, H01L27/146P5, H01L27/146A8S, G01T1/36G|
|May 4, 2004||AS||Assignment|
Owner name: GENERAL ELECTRIC COMPANY, NEW YORK
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:WEAR, JAMES A.;WASHENKO, ROBERT A.;REEL/FRAME:015304/0614
Effective date: 20040408
|Feb 13, 2007||CC||Certificate of correction|
|Jun 7, 2010||FPAY||Fee payment|
Year of fee payment: 4
|Jun 5, 2014||FPAY||Fee payment|
Year of fee payment: 8